1. Field of the Invention
The present invention relates to a semiconductor device having a metal film wiring on an insulating film. More particularly, the present invention relates to a semiconductor device having improved adhesivity between the metal film wiring and the insulating film, and to a process for production of such a semiconductor device.
2. Description of the Related Art
As integrated circuits become finer and wiring-to-wiring intervals become a sub-micron level, the capacity between wirings increases sharply; as a result, delay in signal transfer by wiring increases and the operational speed of integrated circuit is affected adversely. Therefore, it has become necessary to reduce the capacity between wirings.
As the insulating film between wirings, a silicon oxide film (SiO.sub.2 film) has been used heretofore. The silicon oxide film has a dielectric constant of about 4.2 to 5.0. For reducing the dielectric constant to lower the capacity between wirings, a method is known which comprises adding fluorine (F) to a silicon oxide film to form a Si-F bond-containing insulating film (see, for example, Extended Abstracts of the 1995 International Conference on Solid State Devices and Materials, 1995, pp. 157-159, "Fluorine Doped SiO.sub.2 for Low Dielectric Constant Films in Sub-Half Micron ULSI Multilevel Interconnection"). The Si-F bond-containing insulating film has a dielectric constant of 3.0 to 3.6 which is lower by about 15 to 40% than that of the silicon oxide film.
The Si-F bond-containing insulating film, however, has poor adhesivity to a titanium (Ti) wiring layer, and the wiring layer is peeled. This problem is described below referring to accompanying drawings.
FIG. 15(a) to FIG. 15(c) are sectional views showing the steps of a process for producing a semiconductor device wherein two wiring layers are formed at the surface and a tungsten plug is formed in the contact hole. As shown in FIG. 15(a), on a substrate 1001 on which transistors, etc. have been formed, is formed a silicon oxide film 1002 as an insulating film; then, a titanium film 1003a, a titanium nitride film 1003b, an aluminum-containing metal film 1003c and a titanium nitride film 1003d are formed in this order, and dry etching is conducted to form a first wiring 1003 in a given pattern. Thereafter, an interlayer insulating film 1004 consisting of a Si-F bond-containing silicon oxide film is formed by high-density plasma CVD, after which part of the interlayer insulating layer 1004 and part of the titanium nitride film 1003d (which is the uppermost layer of the first wiring 1003) are selectively removed by dry etching to form a contact hole 1005 reaching part of the first wiring 1003.
Next, as shown in FIG. 15(b), a titanium film 1007a and a titanium nitride film 1007b are formed in this order; then, the substrate is heated to about 450.degree. C. and a tungsten film 1006a is formed by blanket tungsten CVD to fill the contact hole 1005 and cover the interlayer insulating film 1004. The titanium film 1007a and the titanium nitride film 1007b are used in order to enhance the adhesivity of the tungsten formed above the interlayer insulating film 1004, even when the interlayer insulating film 1004 is a F-free silicon oxide film. The titanium film 1007a also has a role of decreasing the contact resistance to the aluminum-containing metal film 1003c of the first wiring 1003 at the bottom of the contact hole 1005.
Next, as shown in FIG. 15(c), dry etching is conducted to remove the portion of the tungsten film 1006a above the interlayer insulating film 1004, other than the contact hole 1005, whereby a tungsten plug 1006b is allowed to remain in the contact hole 1005. Then, an aluminum-containing metal film 1007c and a titanium nitride film 1007d are formed in this order, and dry etching is conducted to form a second wiring 1007 in a given pattern.
In this process, however, when a tungsten film 1006a is formed at a substrate temperature of about 450.degree. C., part of the titanium film 1007a and part of the F contained in the interlayer insulating film 1004 react with each other to form a Ti-F compound, deteriorating the adhesivity between the titanium film 1007a and the interlayer insulating film 1004. Further, peeling occurs between the titanium film 1007a and the interlayer insulating film 1004 owing to the stress of the tungsten film 1006a.
A solution to this peeling is disclosed in Japanese Patent Application Kokai (Laid-Open) No. 321547/1996. FIG. 16(a) to FIG. 16(c) are sectional views showing the steps of a process for producing a semiconductor device free from the above peeling.
As shown in FIG. 16(a), on a substrate 1101 on which transistors, etc. have been formed, is formed a silicon oxide film 1101 as an insulating film; then, a titanium film 1103a, a titanium nitride film 1103b and an aluminum-containing metal film 1103c are formed in this order, and dry etching is conducted to form a first wiring 1103 in a given pattern. Thereafter, an interlayer insulating film (consisting of a Si-F bond-containing silicon oxide film) and an interlayer insulating film 1104b (consisting of a F-free silicon oxide film) are formed in this order by high-density plasma CVD to form an interlayer insulating film 1104. Then, dry etching is conducted to selectively remove part of the interlayer insulating film 1104 to form a contact hole 1105 reaching part of the first wiring 1103.
Next, as shown in FIG. 16(b), a tungsten film 1106 is formed only in the contact hole 1105 by selective tungsten CVD. The above-mentioned titanium film 1007a and titanium nitride film 1007b, which are used for enhancing the adhesivity of the tungsten formed above the interlayer insulating film, are not required in this process because the tungsten film 1006 is formed only in the contact hole 1105.
Next, as shown in FIG. 16(c), a titanium film 1107a, a titanium nitride film 1107b and an aluminum-containing metal film 1107c are formed in this order, after which dry etching is conducted to form a second wiring 1107 in a given pattern.
Thus in the semiconductor device produced by the above process, the Si-F bond-containing silicon oxide film and the titanium film make no direct contact with each other; therefore, there takes place no peeling of the metal film wiring. In the process, however, since the tungsten film 1106 is formed directly on the aluminum-containing metal film 1103c, the resistance at the boundary of the two films is large.
Meanwhile, in recent years, in order to make small the resistance of plug in contact hole, it has become important to form the plug with an aluminum alloy having a specific resistance smaller than that of tungsten. Below is described a process for producing a semiconductor device wherein an aluminum-containing metal plug is formed in the contact hole.
FIG. 17(a) to FIG. 17(c) are sectional views showing the steps of a process for producing a semiconductor device wherein a two-layer wiring is formed at the surface and an aluminum-containing metal plug is formed in the contact hole between the two wiring layers.
As shown in FIG. 17(a), on a substrate 1201 on which transistors, etc. have been formed, is formed a silicon oxide film 1202 as an insulating film. Then, a titanium film 1203a, a titanium nitride film 1203b, an aluminum-containing metal film 1203c and a titanium nitride film 1203d are formed in this order, after which dry etching is conducted to form a first wiring 1203 in a given pattern. Next, an interlayer insulating film 1204 consisting of a Si-F bond-containing silicon oxide film is formed by high-density plasma CVD. Thereafter, dry etching is conducted to selectively remove part of the interlayer insulating film 1204 and part of the titanium nitride film 1203d which is the uppermost layer of the first wiring 1203, whereby a contact hole 1205 reaching part of the first wiring 1203 is formed.
Next, as shown in FIG. 17(b), a titanium film 1206a is formed. Then, an aluminum-containing metal film 1206b is formed by sputtering, in a state that the substrate 1201 has been heated to about 450.degree. C., whereby the contact hole 1205 is filled and the interlayer insulating film 1204 is covered by the aluminum-containing metal film 1206b. Here, the titanium film 1206a serves to make easy the filling of the aluminum-containing metal film 1206b in the contact hole 1205.
Next, as shown in FIG. 17(c), a titanium nitride film 1206c is formed, after which dry etching is conducted to form a second wiring 1206 in a give pattern.
In the above process, however, when an aluminum-containing metal film 1206b is formed at a substrate temperature of about 450.degree. C., part of the titanium film 1206a and part of the F contained in the interlayer insulating film 1204 react with each other to form a Ti-F compound; as a result, the adhesivity between the titanium film 1206a and the interlayer insulating film 1204 is deteriorated and peeling takes place at the boundary of the two films.
Thus, in using an aluminum-containing metal plug having a small specific resistance, there is a problem of the above-mentioned peeling.